This invention relates to a ceramic sheet formed by subjecting inorganic fine particles to a sheet-making treatment. More particularly, the present invention relates to a ceramic sheet formed by fixing fine inorganic particles to cellulose pulp and also to a method for producing the same.
Various methods have heretofore been proposed in order to produce a ceramic sheet from a mixed suspension of various fine inorganic particles and cellulose pulp by using a conventional paper-making process. Among them, there are a method which adds an inorganic flocculant, such as alumina sulfate, or an organic high-molecular flocculant, such as polyethyleneimine or cationmodified starch, to the suspension to convert the fine inorganic particles into macro-particles and thus to fix them to the cellulose pulp, and a method which adds a surfactant to the cellulose pulp so as to uniformly disperse the fine inorganic particles and to fix them onto the cellulose pulp. In accordance with these methods, however, when large quantities such as 50 wt.% or more of the fine inorganic particles on the dry basis weight of the sheet are to be contained in the ceramic sheet, the proportion of the inorganic particles not coming into contact with the cellulose pulp becomes greater so that the fine inorganic particles are likely to peel off from the sheet after sheet making. Furthermore, if the amount of the flocculant or the surfactant is increased in order to increase the fixing ratio of the inorganic particles to the cellulose pulp, flocks of the inorganic particles are formed so that the distribution of the inorganic particles in the sheet becomes non-uniform and, at the same time, a sheet as thin as 0.5 mm or below becomes difficult to be produced.
Possible applications of this kind of ceramic sheet include a flame retardant material, an electrical insulating material and a heat insulating material in the form of the ceramic sheet as it is, and a sintered ceramic sheet after the ceramic sheet is sintered. In producing the sintered body by sintering the ceramic sheet, cellulose pulp in the sheet is burnt out and sinterable inorganic particles are sintered into a firm, sintered ceramic sheet. The conventional ceramic sheet, however, undergoes remarkable firing shrinkage in a wide temperature range from burning of the cellulose pulp before sintering of the inorganic particles so that the sintered sheet is not free from occurrence of cracks and is likely to be broken.